Carbon Dioxide (CO2) emitted from power plants is considered to be a greenhouse gas that needs to be removed and sequestered. In the present Integrated Gasification Combined Cycle (IGCC) technology pre-combustion capture of CO2 is preferred. IGCC plants with CO2 capture and removal currently employ a physical solvent such as SELEXOL™, a trademark of Union Carbide Corporation, by absorption/de-absorption process for capturing and removing carbon as carbon dioxide from syngas fuel. More specifically, syngas produced from the gasifier is sent to a set of shift reactors in order to convert CO into CO2 and H2. Then with the use of a physical solvent such as SELEXOL™, CO2 is captured. After de-absorption the captured CO2 can be recovered.
Carbon dioxide removed by this process comes out as a gaseous product at low pressure (15 to 300 psia). This recovered CO2 needs to be stored in liquid state at high pressures (on the order of 2000 psia). Thus, the gaseous CO2 is pressurized and then cooled using refrigerants. This liquefies the gas and then it is pumped to high pressures.
The gaseous compression of carbon dioxide requires large amounts of auxiliary compression power, which results in lower plant net output and efficiency.
FIG. 1 depicts a Block Flow Diagram of a typical IGCC system involving CO2 capture based on the current art and includes the following major process steps:    A. A high pressure Radiant Only Gasifier 10 with water quench of the syngas to maximize sensible heat recovery.    B. An air separation unit 12 to produce 95% purity oxygen required for gasification using Elevated Pressure (EP) ASU with partial air extraction from the GT.    C. A single/two stage catalytic Water-Gas-Shift reactor 14 to produce a predominantly H2-CO2 rich gas.    D. Product gas cleaning, H2S removal and sulfur recovery 16 and to capture CO2 present in the fuel thus de-carbonizing the fuel going to the Gas Turbine 18.    E. Power generation using an advanced syngas-fueled gas turbine power cycle.
The current art uses a two-column acid gas removal (AGR) system 20 to selectively remove H2S and CO2 from the shifted syngas.
FIG. 2 illustrates the present two-column AGR system 20. The encircled portion of the scheme relates to recovery of the captured CO2 from the physical solvent. In the current art, as depicted in the FIG. 3, the configuration has three different pressure stages 22,24,26 in order to flash out the CO2 gas from the physical solvent 28.